Optical probe for optical imaging system

ABSTRACT

Methods and apparatus for monitoring oxygen saturation levels in tissue are disclosed. According to one aspect of the present invention, a sensor arrangement for use in an optical imaging system includes a first source structure, a second source structure, and a detector arrangement. The first source structure provides a first beam of light and the second source structure provides a second beam of light. The detector arrangement includes detector structures that have centerpoints, and receives the first and second beams of light after the first and second beams of light are reflected off of an external surface. The detector arrangement is arranged to define a first axis that passes through the centerpoint of each detector structure, and a distance from a centerpoint of the first source structure to the first axis is not equal to a distance from a centerpoint of the second source structure to the first axis.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to optical imaging systems that monitor oxygen levels in tissue. More specifically, the present invention relates to optical probes that include sources and detectors that are not symmetrically arranged on sensor heads of the optical probes.

2. Description of the Related Art

Near-infrared spectroscopy has been used for non-invasive measurement of various physiological properties in animal and human subjects. The basic principle underlying the near-infrared spectroscopy is that physiological tissues include various highly-scattering chromophores to the near-infrared waves with relatively low absorption. Many substances in a medium may interact or interfere with the near-infrared light waves propagating therethrough. Human tissues, for example, include numerous chromophores such as oxygenated hemoglobin, deoxygenated hemoglobin, water, lipid, and cytochrome, where the hemoglobins are the dominant chromophores in the spectrum range of approximately 700 nm to approximately 900 nm. Accordingly, the near-infrared spectroscope has been applied to measure oxygen levels in the physiological medium such as tissue hemoglobin oxygen saturation and total hemoglobin concentrations.

Various techniques have been developed for the near-infrared spectroscopy, e.g., time-resolved spectroscopy (TRS), phase modulation spectroscopy (PMS), and continuous wave spectroscopy (CWS). In a homogeneous and semi-infinite model, both TRS and PMS have been used to obtain spectra of an absorption coefficient and reduced scattering coefficient of the physiological medium by solving a photon diffusion equation, and to calculate concentrations of oxygenated and deoxygenated hemoglobins as well as tissue oxygen saturation. CWS has generally been designed to solve a modified Beer-Lambert equation and to measure changes in the concentrations of oxygenated and deoxygenated hemoglobins.

Despite their capability of providing the hemoglobin concentrations as well as the oxygen saturation, one major drawback of TRS and PMS is that the equipment is bulky and expensive. CWS may be manufactured at a lower cost but is limited in its utility because it cannot compute the oxygen saturation from the changes in the concentrations of oxygenated and deoxygenated hemoglobins.

Optical Diffusion Imaging and Spectroscopy (ODIS) allows tissue to be characterized based on measurements of photon scattering and absorption. In tissue such as human tissue, near infrared light is highly scattered and minimally absorbed. Optical diffusion imaging is achieved by sending optical signals into tissue and measuring the corresponding diffuse reflectance or transmittance on the tissue surface.

Scattering is caused by the heterogeneous structure of a tissue and, therefore, is an indicator of the density of a cell and the nuclear size of the cell. Absorption is caused by interaction with chromophores. ODIS emits light into tissue through a sensor. The position of the light source which emits the light and a detector which detects the light allows a depth of measurement to be determined. A ratio of oxyhemoglobin and deoxyhemoglobin may be used to allow for substantially real-time measurement of oxygen, e.g., oxygen saturation levels.

Within ODIS systems, sensors which come into contact with tissue surfaces generally have optical fibers arranged thereon in a substantially symmetric layout. That is, optical fibers that are coupled to light sources are arranged in a substantially symmetric orientation relative to optical fibers that are coupled to light detectors. While a symmetric orientation is effective in allowing for oxygen saturation levels to be measured, the manufacture of such sensor is often difficult, as the exact placement of the optical fibers within the sensor is crucial. Further, when the anatomy of tissue or underlying structure is not substantially symmetric, the use of a sensor with a symmetric orientation may not allow for accurate measurements to be readily made.

Therefore, what is needed is a sensor that is relatively easy to manufacture, and is arranged to be used on tissue which may not have a symmetric anatomy. That is, what is desired is a sensor with a layout of optical fibers for light sources and optical fibers for detectors that facilitates use with tissue having substantially any anatomy.

SUMMARY OF THE INVENTION

The present invention relates to a probe with a sensor that supports source fibers and detector fibers such that the source fibers have a substantially non-symmetric arrangement relative to the detector fibers. According to one aspect of the present invention, a sensor arrangement that is suitable for use in an optical imaging system and is arranged to contact a body such as tissue includes a first source structure, a second source structure, and a detector arrangement. The first source structure provides a first beam of light and the second source structure provides a second beam of light. The detector arrangement includes detector structures that each have a centerpoint, and receives the first beam of light and the second beam of light after the first beam of light and the second beam of light are reflected off of the body. The detector arrangement is arranged to define a first axis that passes through the centerpoint of each detector structure, and a distance from a centerpoint of the first source structure to the first axis is not equal to a distance from a centerpoint of the second source structure to the first axis.

In one embodiment, a difference between the distance from the centerpoint of the first source structure to the first axis and the distance from the centerpoint of the second source structure is at least approximately 0.03 millimeters. In such an embodiment, the distance from the centerpoint of the first source structure to the first axis may be approximately 0.020 millimeters and the distance from the centerpoint of the second source structure to the first axis may be approximately 0.24 millimeters.

A probe with a sensor or a sensor head that has source structures in a non-symmetric orientation with respect to detector structures enables the sensor head to be utilized to monitor tissue with an underlying anatomy that is not substantially symmetric. The lack of symmetry also effectively loosens manufacturing tolerances associated with the manufacture of such sensor. Any attenuation associated with the offset orientation of optical fibers that are coupled to light sources is typically compensated for through the use of software code devices executing with respect to an optical imaging system. Hence, the amount of compensation applied may be relatively easily varied as needed to accommodate inaccuracies in the positioning of optical fibers with respect to the sensor.

According to another aspect of the present invention, a sensor arrangement that is suitable for use in an optical imaging system includes a first source structure that is arranged to provide a first beam of light and a second source structure that is arranged to provide a second beam of light. The sensor arrangement also includes a detector arrangement that has a first detector structure with a first centerpoint and a second detector structure with a second centerpoint. The detector arrangement is arranged to receive the first beam of light and the second beam of light after the first beam of light and the second beam of light are reflected off of a body. An orientation of the first source structure with respect to the detector arrangement is not symmetric relative to an orientation of the second source structure with respect to the detector arrangement.

According to yet another aspect of the present invention, a method for taking an oxygen saturation measurement of tissue using an optical system that utilizes a probe with a sensor head in which a first source structure and a second source structure are offset relative to detector structures involves positioning the sensor head in contact with the tissue and transmitting light into the tissue through the first source structure and the second source structure. The method also involves receiving reflected light from the tissue at the detector structures that includes attenuation characteristics, and processing the reflected light using a plurality of photodetectors. Processing the reflected light using the plurality of photodetectors includes compensating for the attenuation characteristics using an attenuation compensator.

In accordance with still another aspect of the present invention, a probe which may be used as a part of an optical system to monitor oxygen levels in tissue includes a coupling interface that allows the probe to be coupled to light sources and detectors. A sensor head of the probe is arranged to contact the tissue, and supports a first source structure, a second source structure, and a detector arrangement. The first source structure and the second source structure are coupled to the light sources via the coupling interface, while the detector arrangement is coupled to the detectors through the coupling interface. An orientation of the first source structure relative to the detector arrangement is not symmetric with respect to an orientation of the second source structure relative to the detector arrangement.

In one embodiment, the detector arrangement includes detector structures that each have a centerpoint. In such an embodiment, the detector arrangement receives the first beam of light and the second beam of light after the first beam of light and the second beam of light are reflected off of the tissue. The detector arrangement defines a first axis that passes through the centerpoint of each detector structure of the plurality of detector structures such that a distance from a centerpoint of the first source structure to the first axis is unequal to a distance from a centerpoint of the second source structure to the first axis.

These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1A is a block diagram representation of an optical imaging system with a sensor head which includes sources in an offset arrangement relative to detectors in accordance with an embodiment of the present invention.

FIG. 1B is a block diagram representation of an optical imaging system with a sensor head which includes sources in an offset arrangement relative to detectors, i.e., optical imaging system 100 of FIG. 1A, in accordance with an embodiment of the present invention.

FIG. 2A is a diagrammatic representation of a sensor head with a pair of light sources that are in an offset arrangement relative to a pair of detectors in accordance with an embodiment of the present invention.

FIG. 2B is a diagrammatic representation of a sensor head with a pair of light sources that are in an offset arrangement relative to a set of four detectors in accordance with a first embodiment of the present invention.

FIG. 2C is a diagrammatic representation of a sensor head with a pair of light sources that are in an offset arrangement relative to a set of four detectors in accordance with a second embodiment of the present invention.

FIG. 3 is a block diagram representation of light sources and detectors that are associated with a sensor head in accordance with an embodiment of the present invention.

FIG. 4 is a process flow diagram which illustrates one method of utilizing a sensor head with light sources that are in an offset arrangement relative to detectors in accordance with an embodiment of the present invention.

FIG. 5 is a diagrammatic representation of an optical imaging system that includes a console and a decoupleable probe with a sensor head with light sources that are in an offset arrangement relative to detectors in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A sensor head which is such that optical fibers that are coupled to light sources are arranged in an offset orientation relative to optical fibers that are coupled to detectors allows the sensor head to be utilized in areas in which tissue being monitored is not substantially symmetric. Any attenuation associated with the offset orientation of optical fibers that are coupled to light sources is typically compensated for through software. Such a sensor head is relatively easy to manufacture in that the placement of optical fibers that are coupled to light sources is less rigid, i.e., any slight variation in the placement of the optical fibers may be corrected for using the software that compensates for attenuation. In addition, the use of software to compensate for attenuation associated with the placement of optical fibers on a sensor head essentially enables the sensor head to be used with both symmetric and asymmetric tissue anatomies.

As will be understood by those skilled in the art, a volume of tissue substantially immediately beneath a sensor head may either be homogeneous or inhomogenous depending upon the actual anatomical structures contained within this volume. By way of example, when a sensor head is positioned on skin overlying a thick region of adipose tissue, the distribution of signet cells and capillaries containing oxygenated hemoglobin is generally relatively uniform, i.e., symmetric and homogenous. However, a sensor head may be positioned over a tissue volume in which underlying structure include arteries, veins, bone, tendon, cartilage, fascia, muscle, or pigmented lesions. Such tissue may have asymmetric anatomies that cause light to be reflected or absorbed asymmetrically due, for example, to regions that are either unusually reflective or absorptive. Software that compensates for attenuation may eliminate readings associated with light that reflects off of structures such as bone. Optical fibers that are coupled to sources and are positioned in a sensor head in an offset orientation relative to optical fibers coupled to detectors may facilitate the transmission and reading of light that avoids structures such as bone. Hence, the use of offset source optical fiber orientations facilitate the creation of specialized sensor heads that may be used to measure oxygen saturation in many different parts of a body.

FIG. 1A is a block diagram representation of an optical imaging system with a sensor head that includes source arrangements arranged in an offset orientation relative to detector arrangements in accordance with an embodiment of the present invention. An optical imaging system 100 includes a unit 104 and a probe 108 that are coupled via a connection interface 112. Connection interface 112 is generally a light-tight interconnection with a laser safety interlock that is arranged to substantially prevent laser light from being emitted through connection interface 112 when probe 108 is not coupled to unit 104. Connection interface 112 typically includes a panel connector (not shown) attached to unit 104 and a cable connector (not shown) attached to probe 108.

Unit 104 includes a first light source 116 and a second light source 120. First light source 116 and second light source 120, in the described embodiment, are each dual wavelength light sources. In other words, first light source 116 provides two wavelengths of light and second light source 120 provides two wavelengths of light. First light source 116 and second light source 120 may each include a laser diode that provides a light beam or pulse at a lower frequency and a laser diode that provides a light beam or pulse at a higher frequency. By way of example, first light source 116 and second light source 120 may each include a laser diode that produces visible red light of an approximately 690 nanometer (nm) wavelength and a laser diode that produces near infra red light of an approximately 830 nm wavelength. It should be appreciated, however, that the wavelengths of light produced by laser diodes associated with first light source 116 and second light source 120 may vary widely.

Light emitted by first light source 116 and light emitted by second light source 120 is provided to a beam combiner 124 via optical fibers (not shown). Each laser diode associated with first light source 116 and each laser diode associated with second light source 120 is provided on a separate optical fiber (not shown). Beam combiner 124 effectively merges the light from the laser diodes of first light source 116 and merges the light from the laser diodes of second light source 120. The merged light is then provided via output fibers (not shown) to connection interface 112. The output fibers are arranged to allow the merged or combined light to be homogenized to ensure that the light is substantially uniformly distributed across the output fibers when the light enters connection interface 112.

Through connection interface 112, light is provided to a sensor head 128 of probe 108. Within sensor head 128, optical fibers (not shown) provide the merged light associated with first light source 116 and the merged light associated with second light source 120 to a surface of sensor head 128 that is arranged to come into contact with tissue 132. The optical fibers (not shown) are positioned such that they have an offset orientation with respect to optical fibers (not shown) that are associated with photodetectors 136 within unit 104. The orientation of source optical fibers and detector optical fibers will be described below with respect to FIGS. 2A-2C.

When sensor head 128 causes light to be transmitted into tissue 132, the reflected light is collected by optical detector fibers (not shown) that are coupled to photodetectors 136. In general, at least two photodetectors 136 are included within unit 104 and are configured to be sensitive to the light which is transmitted by first light source 116 and second light source 120. An attenuation compensator 140 within unit 104 is generally arranged to compensate for any attenuation in the reflected light that results from the offset orientation of source optical fibers (not shown) relative to detector optical fibers (not shown). In one embodiment, attenuation compensator 140 effectively provides compensation using a mathematical algorithm that constructs ratios in which attenuation coefficients may be found in both a numerator and a denominator and hence, may be cancelled out. Such ratios may use light intensities as detected by photodetectors 136 in such a way that attenuation factors have little effect on the evaluation of optical properties of tissue 132 beneath sensor head 128. It should be appreciated that attenuation compensator 140 may generally be substantially incorporated into software or firmware that executes an algorithm that determines oxygen saturation levels.

FIG. 1B is a block diagram representation of optical imaging system 100 of FIG. 1A which shows the path of light emitted by light sources, i.e., first light source 116 and second light source 120 of FIG. 1A, in accordance with an embodiment of the present invention. When first light source 116 emits light at two wavelengths, light of the first wavelength 152 a and light of the second wavelength 152 b are provided to beam combiner 124 which effectively merges the light into a light stream 152 c that is provided to sensor head 128, e.g., through optical source fibers. Similarly, when second light source 120 emits light at two wavelengths, light of the first wavelength 156 a and light of the second wavelength 156 b are merged into a light stream 156 c by beam combiner 124 that is provided to sensor head 128. Light streams 152 c, 156 c are transmitted into tissue 132 reflect off of tissue 132, through sensor head 128 to photodetectors 136.

As previously mentioned, optical source fibers are arranged such that at a surface of a sensor head that is arranged to come into contact with tissue, the optical source fibers have an offset orientation relative to optical detector fibers. With reference to FIG. 2A, the orientation of source fibers with respect to detector fibers will be described in accordance with an embodiment of the present invention. A sensor head 200, which may be of substantially any shape or size, is a part of a probe that is a part of an overall system that measures oxygen saturation levels in tissue. Sensor head 200 is arranged to accommodate source arrangements 204 a, 204 b, and detector arrangements 208 a, 208 b. For ease of discussion, although source arrangements 204 a, 204 b are generally fiberoptic cables or optical fibers coupled to light sources and detector arrangements 208 a, 208 b are generally fiberoptic cables or optical fibers coupled to photodetectors, source arrangements 204 a, 204 b are referred to herein as sources and detector arrangements 208 a, 208 b are referred to herein as detectors.

Sources 204 a, 204 b are arranged such that they are in an offset arrangement relative to detectors 208 a, 208 b. That is, source 204 a and source 204 b are not equidistant to detectors 208 a, 208 b relative to at least one axis. Detectors 208 a, 208 b are arranged such that a centerline 214 of detectors 208 a, 208 b is approximately parallel to an x-axis 212 a. Typically, centerline 214 passes through a centerpoint of each detector 208 a, 208 b. Sources 204 a, 204 b are arranged such that a centerline 216 of source 204 a is parallel to a centerline 218 of source 204 b, but is not coincident with centerline 218. Centerline 216 passes through a centerpoint of source 204 a and is parallel to x-axis 212 a, while centerline 216 passes through a centerpoint of source 204 b and is parallel to x-axis 212 b.

A distance y1 between centerline 214 and centerline 216 along a y-axis 212 b differs from a distance y2 between centerline 214 and centerline 218. Although distance y2 is shown as being greater than distance y1, it should be appreciated that distance y1 may instead be greater than y2. The difference between distance y2 and distance y1 is generally characteristic of the offset arrangement, or substantially unbalanced arrangement, of sources 204 a, 204 b relative to detectors 208 a, 208 b. In other words, there is effectively a lack of symmetry in the placement of sources 204 a, 204 b.

In general, more than two detectors may be used in conjunction with a pair of detectors to monitor oxygen saturation in tissue. By way of example, three or four detectors may be used to detect light that is provided by a pair of sources and is reflected off of a tissue surface. It should be appreciated that some of the light may be reflected from tissue at various depths beneath the tissue surface. That is, light may be reflected off the tissue surface and off of tissue that underlies the surface. The tissue that underlies the surface and allows light to be reflected may be as deep as approximately one centimeter below the surface of the tissue. FIG. 2B is a diagrammatic representation of a sensor head which is arranged to include a pair of sources or, more specifically, source arrangements and four detectors or, more specifically, detector arrangements, in accordance with an embodiment of the present invention. A sensor head 220 includes four detectors 228 a-d which are arranged such that centerpoints of detectors 228 a-d are substantially aligned along a centerline 234 that is substantially parallel to an x-axis 232 a. Sensor head 220 also includes sources 224 a, 224 b which each include a centerpoint. A centerline 236 that is parallel to x-axis 232 a passes through the centerpoint of source 224 a, and a centerline 238 that is parallel to x-axis 232 a passes through the centerpoint of source 224 b.

In the described embodiment, a distance y1 along a y-axis 232 b between centerline 234 and centerline 236 is not equal to a distance y2 along y-axis 232 b between centerline 234 and centerline 238. Distance y1 may be approximately 0.2 millimeters (mm), as for example approximately 0.197 mm, while distance y2 may be approximately 0.24 mm, as for example 0.236 mm. It should be appreciated that distance y1 and distance y2 may vary widely depending upon any number of factors. The factors include, but are not limited to, the overall size of sources 224 a, 224 b and detectors 228 a-d, the overall size of sensor head 220, and the application for which sensor head 220 is intended. While distance y2 is shown as being greater than distance y1, distance y1 may instead be greater than distance y2. In general, the difference between distance y2 and distance y1 is at least approximately 0.3 mm. For example, distance y2 and distance y1 may differ by approximately 1.0 mm.

The positioning of sources 224 a, 224 b and detectors 228 a-d may vary widely. By way of example, for an embodiment in which sources 224 a, 224 b and detectors 228 a-d are each approximately one mm in diameter, centerpoints of sources 224 a, 224 b may be separated by a distance d2 that is approximately 0.22 mm relative to x-axis 232 a and by a distance y4 that is approximately 0.04 mm. Detectors 228 a-d may be arranged such that centerline 234 is offset from a top edge of sensor head 220 by a distance y3 that is approximately 0.06 mm, and such that adjacent detectors 228 a-d are separated by a distance d1 that is between approximately 0.06 mm to approximately 0.07 mm. Sensor head 220 may have a width of approximately 0.34 mm along x-axis 232 a and a height of approximately 0.49 mm along y-axis 232 b when detectors 228 a-d and sources 224 a, 224 b are spaced as described above. However, sensor head 220 generally has dimensions that may vary widely, e.g., dimensions which may vary depending upon the application for which sensor head 220 is intended.

While a lack of symmetry in the positioning of sensors relative to detectors has been described as being such that distances between sensors and detectors are not equal relative to a y-axis, a lack of symmetry may instead or additionally have a lack of symmetry relative to an x-axis. Referring next to FIG. 2C, a sensor head that includes a pair of sources which are in an offset arrangement relative to a set of four detectors with respect to an x-axis will be described. A sensor head 240 includes four detectors 248 a-d, although the number of detectors 248 a-d may vary. Detectors 248 a-d are arranged such that a centerline 254 is substantially parallel to an x-axis 252 a and passes through the centerpoint of each detector 248 a-d. A first detector 248 a and a last detector 248 d, i.e., the detectors which are farthest apart relative to x-axis 252 a, are used to define a central bisecting line 262 of detectors 248 a-d. Central bisecting line 262 is parallel to a y-axis 252 b, and is arranged such that a distance x3 from the centerpoint of detector 248 a to central bisecting line 262 is substantially equal to a distance x4 from the centerpoint of detector 248 d to central bisecting line 262. That is, central bisecting line 262 is arranged to pass through a central midpoint between the centerpoint of detector 248 a and the centerpoint of detector 248 d such that central bisecting line 262 is substantially perpendicular to centerline 254.

As shown, a centerpoint of a first source 244 a and the centerpoint of first detector 248 a are aligned along a centerline 257 that is substantially parallel to a y-axis 252 b. Similarly, a centerpoint of a second source 244 b and the centerpoint of last detector 248 d are aligned along a centerline 259 that is substantially parallel to y-axis 252 b. It should be appreciated, however, that centerline 257 may not necessarily pass through the centerpoint of first detector 248 a, and centerline 259 may not necessarily pass through the centerpoint of last detector 248 d. That is, centerline 257 is effectively a line that is substantially parallel to y-axis 252 b and passes through first source 244 a, while centerline 259 is effectively a line that is substantially parallel to y-axis 252 b and passes through second source 244 b.

A distance x1 between centerline 257 and central bisecting line 262 is not equal to a distance x2 between centerline 259 and central bisecting line 262. In other words, first source 244 a and second source 244 b are not equidistant from central bisecting line 262. Hence, sources 244 a, 244 b are positioned in an offset or unbalanced orientation relative to x-axis 252 a.

Sources are typically arranged to emit light of specific wavelengths. As discussed above, light of a lower wavelength emitted by a source may have a wavelength of approximately 690 nm, while light of a higher wavelength emitted by the source may have a wavelength of approximately 830 nm. FIG. 3 is a block diagram representation of light sources and detectors that are associated with a sensor head in accordance with an embodiment of the present invention. A first source may include a laser diode 302 a that produces light at a wavelength of approximately 690 nm as well as a laser diode 302 b that produces light at a wavelength of approximately 830 nm. Similarly, a second source may include a laser diode 306 a that produces light at a wavelength of approximately 690 nm as well as a laser diode 306 b that produces light at a wavelength of approximately 830 nm.

A beam combiner 310 is arranged to enable light emitted by laser diodes 302 a, 302 b to be merged onto an optical fiber 312 that is provided to a sensor head 322. Beam combiner 310 is also arranged to enable light emitted by laser diodes 306 a, 306 b to be merged onto an optical fiber 316 that is provided to sensor head 322. Light transmitted by fibers 312, 316 through a tissue or other surface is reflected, and the reflected light is effectively captured on optical fibers 324 which provide the reflected light to photodetectors 318. Photodetectors 318 are arranged to be sensitive to light with wavelengths of approximately 690 nm and approximately 830 nm, and typically have a relatively high gain.

With reference to FIG. 4, one method of monitoring oxygen saturation in tissue using an oximeter with a sensor head in which sources are in an offset orientation relative to detectors will be described in accordance with an embodiment of the present invention. A process 400 of using an oximeter begins at step 404 in which a probe, i.e., a probe that includes a sensor head in which sources are positioned in an offset orientation relative to detectors, is applied against tissue. Once the sensor head is positioned in contact with tissue, a first source S1 associated with the probe sends a lower wavelength pulse of light into the tissue in step 408. The first source S1 may include a laser diode that produces an approximately 690 nm wavelength of visible red light, as discussed above, although the lower wavelength of light produced by the first source S1 may vary. In general, first source S1 is a source arrangement that produces light at two wavelengths. Hence, first source S1 may include two substantially separate laser diodes that produce light at two wavelengths.

In step 412, a detector arrangement associated with the probe detects the approximately 690 nm light. As discussed above, when the approximately 690 nm light is transmitted into the tissue, the approximately 690 nm light is reflected into the detector arrangement such that the detectors, e.g., the photodetectors, included in the detector arrangement collect the reflected light. A second source S2 then sends a lower wavelength pulse of light in step 416 which, in the described embodiment, is an approximately 690 nm pulse of light. The detector arrangement detects and collects the approximately 690 nm reflected light in step 420.

Once the lower wavelength light is transmitted by both the first source S1 and the second source S2, the first source S1 sends a higher wavelength pulse of light into the tissue in step 424. The higher wavelength pulse of light may be an approximately 830 nm near infrared light produced by a laser diode included in first source S1. After the approximately 830 nm pulse of light is transmitted into the tissue and reflected, the process flow moves to step 428 in which the detector arrangement detects the reflected light.

The second source S2 sends a higher wavelength pulse of light, e.g., light with an approximately 830 nm wavelength, in step 432 that is then reflected off of the tissue and reflected into the detector arrangement in step 436. Once the detector arrangement has received reflected light from both sensors at both the lower wavelength and the higher wavelength, the data acquisition arrangement of the oximeter processes information associated with the received reflected light in step 440. Processing the received reflected light may include executing software or firmware that accounts for or otherwise compensates for attenuation associated with the reflected light in order to determine an oxygen level associated with the tissue. Once the data acquisition arrangement processes the information, the process of monitoring an oxygen saturation level of tissue is completed. It should be understood, however, the steps of FIG. 4 may be repeated to allow for the substantially continuous monitoring of an oxygen saturation level.

An oximeter which utilizes a probe with a sensor head of the present invention may include a portable console unit to which the probe may be coupled. As shown in FIG. 5, a console 500 may include a screen 504 that is arranged to display the oxygen saturation level of tissue that is being monitored. Screen 504, which may be a touchscreen, may also be arranged to indicate when a probe 520 is in use and to provide warnings to a user that indicate when a monitored oxygen saturation level is potentially problematic.

Console 500 includes a panel connector 508 to which a connector 528 of probe 520 may be connected to allow a sensor head 530 of probe 520 to be used to monitor oxygen saturation levels. Fiberoptic cables (not shown) which are used to allow light to pass between connector 528 and sensor head 530 of probe 520 are substantially encased in a cable jacket 534. Console 500 and probe 520 may be a part of the Odyssey Tissue Oximeter available commercially from ViOptix, Inc. of Fremont, Calif.

Although only a few embodiments of the present invention have been described, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or the scope of the present invention. By way of example, the wavelengths emitted by light sources have been described as being approximately 690 nm and approximately 830 nm. However, substantially any wavelengths may be emitted by the light sources.

The probe on which a sensor head is mounted may have a variety of different configurations. For example, the probe may include a handpiece which facilitates spot measurements of tissue. Additionally, the configuration of a sensor head may also vary depending upon the particular application for which the sensor head is to be used.

A probe, e.g., a fiberoptic probe, on which a sensor head is mounted uses fiberoptic cable to carry an optical signal to and from tissue. The fiberoptic cable may be of any length, and may contain one dual wavelength source fiber for each source and one detector fiber for each detector. In one embodiment, the fiberoptic cable may be approximately three meters long, and the source and detector fibers may each have diameters of approximately one mm.

A centerpoint of a source optical fiber and a centerpoint of a detector optical fiber have generally been described as being centerpoints of fibers that are substantially circular in orientation. It should be appreciated that in some instances, when a fiber is not substantially circular in orientation, the centerpoint may be an approximate centerpoint of the fiber.

The steps associated with the various methods of the present invention may be widely varied. Steps may be added, altered, removed, and reordered without departing from the spirit or the scope of the present invention. Therefore, the present examples are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims. 

1. A device comprising: a first source structure, the first source structure being positioned to provide a first beam of light; a second source structure, the second source structure being positioned to provide a second beam of light, and a detector arrangement including a plurality of detector structures, the detector arrangement being positioned to receive the first beam of light after the first beam of light has been transmitted through a tissue, and to receive the second beam of light after the second beam of light has been transmitted through the tissue, wherein the detector arrangement is arranged to define a first axis that passes through a centerpoint of each of the detector structures, a centerpoint of the first source structure to the first axis defines a first line segment, a centerpoint of the second source structure to the first axis defines a second line segment, which is parallel to the first line segment, and lengths of the first and second line segments are not equal.
 2. The device of claim 1 wherein the first source structure comprises a first optical cable coupled to a first light source, and the second source structure comprises a second optical cable coupled to a second light source.
 3. The device of claim 1 wherein the plurality of detector structures comprises a plurality of optical detector cables coupled to a plurality of photodetectors.
 4. A medical device system comprising the device of claim 1 wherein the device is a probe.
 5. The device of claim 1 wherein a difference in length between the first line segment and the second line segment is at least approximately 0.03 millimeters.
 6. The device of claim 1 wherein the first source structure has a diameter of approximately one millimeter, the second source structure has a diameter of approximately one millimeter, and each detector structure of the plurality of detector structures has a diameter of approximately one millimeter.
 7. The device of claim 1 wherein the first line segment has a length of approximately 0.020 millimeters, and the second line segment has a length of approximately 0.24 millimeters.
 8. The device of claim 1 wherein the tissue comprises human tissue.
 9. A device comprising: a first source structure, the first source structure being positioned to provide a first beam of light; a second source structure, the second source structure being positioned to provide a second beam of light; and a detector arrangement, including a plurality of detector structures, each comprising optical fiber, the detector arrangement being positioned to receive the first beam of light after the first beam of light has been transmitted through a tissue, and to receive the second beam of light after the second beam of light has been transmitted through the tissue, wherein the first source structure, the second source structure, a first detector structure, and a second detector structure define vertices of a convex quadrilateral, a first side of the quadrilateral between the first source structure and second source structure is greater in length than a second side of the quadrilateral between the first detector structure and the second detector structure, and a third side of the quadrilateral between the first source structure and first detector structure is greater in length than a fourth side of the quadrilateral between the second source structure and the second detector structure.
 10. The device of claim 9 wherein the tissue comprises human tissue.
 11. The device of claim 9 wherein the first source structure comprises a first optical cable coupled to a first light source, and the second source structure comprises a second optical cable coupled to a second light source.
 12. The device of claim 9 wherein the optical fiber of the detector structures are coupled to a plurality of photodetectors.
 13. A medical device system comprising the device of claim 9 wherein the device is a probe.
 14. The device of claim 9 wherein the first source structure has a diameter of approximately one millimeter, the second source structure has a diameter of approximately one millimeter, and each detector structure of the plurality of detector structures has a diameter of approximately one millimeter.
 15. A method of measuring oxygen saturation of a tissue comprising: positioning a sensor head to face toward the tissue, wherein the sensor head comprises a first source structure, a second source structure, a first detector structure, and a second detector structure that define vertices of a convex quadrilateral, a first side of the quadrilateral between the first source structure and first detector structure has a different length than a second side of the quadrilateral between the second source structure and second detector structure, and the first and second detector structures comprise optical fiber; transmitting light from a system unit through the first source structure and the second source structure into the tissue; receiving light transmitted through the tissue and the detector structures at photodetectors in the system unit, the received light including attenuation characteristics; and processing the received light using the system unit.
 16. The method of claim 15 wherein the attenuation characteristics are caused by the difference in length between the first and second sides of the quadrilateral.
 17. A probe, the probe being adapted for use as a part of a medical device system for measuring oxygen levels in a tissue, the probe comprising: a coupling interface, the coupling interface being adapted to allow the probe to be coupled to a plurality of light sources and a plurality of photodetectors, wherein the light sources and photodetectors are external to the probe; and a sensor head comprising a first source structure, a second source structure, and a detector arrangement, the first source structure and the second source structure being arranged to be coupled to the plurality of light sources via the coupling interface, the detector arrangement being arranged to be coupled to the plurality of photodetectors through the coupling interface, wherein first and second detector structures of the detector arrangement and the source structures have the same cross-sectional area.
 18. The probe of claim 17 wherein the first source structure and the second source structure are arranged to provide light from the plurality of light sources to the tissue, and the detector arrangement is arranged to provide the light transmitted through the tissue to the photodetectors.
 19. The probe of claim 17 wherein the detector arrangement is arranged to receive the first beam of light and the second beam of light after the first beam of light and the second beam of light are transmitted through the tissue.
 20. The device of claim 1 wherein the received second beam of light is received by the detector arrangement after the received first beam of light.
 21. The device of claim 1 wherein the received first beam of light is received by the detector arrangement after the received second beam of light.
 22. The device of claim 1 wherein shapes of the first source structure, second source structure, and the detector structures are the same.
 23. The device of claim 1 wherein cross-sectional areas of the first source structure, second source structure, and the detector structures are the same.
 24. The device of claim 1 wherein shapes of the first source structure, second source structure, and the detector structures are circles.
 25. The device of claim 1 wherein the detector arrangement comprises four detector structures having centerpoints along the first axis.
 26. The device of claim 25 wherein the source and detector structures have the same cross-sectional shape and cross-sectional area.
 27. The device of claim 26 wherein the source and detector structures are on the same plane.
 28. The device of claim 26 wherein the source and detector structures are positioned on a bottom side of a rectangular planar surface.
 29. The device of claim 28 wherein the first axis is parallel to an edge of the rectangular planar surface.
 30. The device of claim 1 wherein each of the detector structures comprises optical fiber.
 31. The device of claim 9 wherein the received second beam of light is received by the detector arrangement after the received first beam of light.
 32. The device of claim 9 wherein the received first beam of light is received by the detector arrangement after the received second beam of light.
 33. The device of claim 9 wherein shapes of the first source structure, second source structure, and the detector structures are the same.
 34. The device of claim 9 wherein cross-sectional areas of the first source structure, second source structure, and the detector structures are the same.
 35. The device of claim 9 wherein shapes of the first source structure, second source structure, and the detector structures are circles.
 36. The device of claim 9 wherein the detector arrangement comprises four detector structures arranged in a line.
 37. The device of claim 36 wherein the first and second detector structures are at ends of the line.
 38. The device of claim 37 wherein there are at most two source structures.
 39. The device of claim 36 wherein the source and detector structures have the same cross-sectional shape and cross-sectional area.
 40. The device of claim 36 wherein the source and detector structures are on the same plane.
 41. The device of claim 36 wherein the source and detector structures are positioned on a bottom side of a rectangular planar surface, and the line is parallel to an edge of the rectangular planar surface.
 42. The device of claim 15 wherein the source and detector structures have the same cross-sectional shape and cross-sectional area.
 43. The device of claim 15 wherein the sensor head further comprises third and fourth detector structures, each comprising optical fiber, arranged in a line with the first and second detector structures, and there are at most two source structures.
 44. The device of claim 15 wherein the sensor head comprises at least three detectors structures, and there are more detector structures than source structures.
 45. The device of claim 15 wherein the source and detector structures are positioned on a bottom side of a rectangular planar surface, the first and second detector structure are arranged in a line, where the line is parallel to a shorter edge of the rectangular planar surface.
 46. The probe of claim 17 wherein the detector arrangement comprises four detector structures, each comprising optical fiber.
 47. The probe of claim 46 wherein the four detector structures are arranged in a line.
 48. The probe of claim 47 wherein a first distance is between the first source structure and the first detector structure, a second distance is between the first source structure and the second detector structure, a third distance is between the second source structure and the first detector structure, a fourth distance is between the second source structure and the second detector structure, a fifth distance is between the first source structure and a third detector structure, a sixth distance is between the first source structure and a fourth detector structure, a seventh distance is between the second source structure and third detector structure, an eighth distance is between the second source structure and fourth detector structure, the first distance is not equal to the second, third, fourth, fifth, sixth, seventh, and eighth distances, the second distance is not equal to the third, fourth, fifth, sixth, seventh, and eighth distances, the third distance is not equal to the fourth, fifth, sixth, seventh, and eighth distances, the fourth distance is not equal to the fifth, sixth, seventh, and eighth distances, the fifth distance is not equal to the sixth, seventh, and eighth distances, the sixth distance is not equal to the seventh, and eighth distances, and the seventh distance is not equal to the eighth distance.
 49. The probe of claim 17 wherein the tissue is human tissue.
 50. The probe of claim 17 wherein the sensor head comprises greater numbers of detector structures than source structures.
 51. The probe of claim 17 wherein the first source structure, second source structure, first detector structure, and second detector structure define vertices of a convex quadrilateral.
 52. The probe of claim 17 wherein a first distance between the first source structure and first detector structure is different from a second distance between the second source structure and the second detector structure.
 53. The probe of claim 17 wherein a first distance between the first source structure and second source structure is greater than a second distance between the first detector structure and the second detector structure, and a third distance between the first source structure and first detector structure is greater than a fourth distance between the second source structure and the second detector structure.
 54. The probe of claim 17 wherein a bottom side of the sensor head comprises a rectangular planar surface, the source and detector structures are positioned on the bottom side, and the first and second detector structures are arranged in a line, where the line is parallel to a shorter edge of the rectangular planar surface.
 55. A device comprising: a first source structure; a second source structure; a first detector structure comprising optical fiber; and a second detector structure comprising optical fiber, wherein the first source structure, second source structure, first detector structure, second detector structure define vertices of a convex quadrilateral, and a first side of the quadrilateral between the first source structure and first detector structure is different in length from a second side of the quadrilateral between the second source structure and the second detector structure.
 56. A device comprising: a first source structure; a second source structure; a first detector structure comprising optical fiber; and a second detector structure comprising optical fiber, wherein the first source structure, second source structure, first detector structure, second detector structure define vertices of a convex quadrilateral, and a first side of the quadrilateral between the first source structure and second source structure is different in length from a second side of the quadrilateral between the first detector structure and the second detector structure.
 57. A device comprising: a first source structure; a second source structure; a first detector structure comprising optical fiber; a second detector structure comprising optical fiber, wherein a first distance is between the first source structure and the first detector structure, a second distance is between the first source structure and the second detector structure, a third distance is between the second source structure and the first detector structure, a fourth distance is between the second source structure and the second detector structure, the first distance is not equal to the second, third, and fourth distances, the second distance is not equal to the third and fourth distances, and the third distance is not equal to the fourth.
 58. The device of claim 55 wherein the first and second source structure comprise optical fiber.
 59. The device of claim 55 wherein cross-sectional shapes of the first source, second source, first detector, and second detector structures are the same.
 60. The device of claim 55 wherein cross-sectional areas of the first source, second source, first detector, and second detector structures are the same.
 61. The device of claim 56 wherein the first and second source structure comprise optical fiber.
 62. The device of claim 56 wherein cross-sectional shapes of the first source, second source, first detector, and second detector structures are the same.
 63. The device of claim 56 wherein cross-sectional areas of the first source, second source, first detector, and second detector structures are the same.
 64. The device of claim 57 wherein the first and second source structure comprise optical fiber.
 65. The device of claim 57 wherein cross-sectional shapes of the first source, second source, first detector, and second detector structures are the same.
 66. The device of claim 57 wherein cross-sectional areas of the first source, second source, first detector, and second detector structures are the same.
 67. The device of claim 57 wherein the first source structure, second source structure, first detector structure, and second detector structure define vertices of a convex quadrilateral.
 68. The device of claim 67 wherein the first and second source structure comprise optical fiber.
 69. The device of claim 67 wherein cross-sectional shapes of the first source, second source, first detector, and second detector structures are the same.
 70. The device of claim 67 wherein cross-sectional areas of the first source, second source, first detector, and second detector structures are the same.
 71. The device of claim 57 comprising: a third detector structure comprising optical fiber; a fourth detector structure comprising optical fiber, wherein a fifth distance is between the first source structure and a third detector structure, a sixth distance is between the first source structure and a fourth detector structure, a seventh distance is between the second source structure and third detector structure, an eighth distance is between the second source structure and fourth detector structure, the first distance is not equal to the second, third, fourth, fifth, sixth, seventh, and eighth distances, the second distance is not equal to the third, fourth, fifth, sixth, seventh, and eighth distances, the third distance is not equal to the fourth, fifth, sixth, seventh, and eighth distances, the fourth distance is not equal to the fifth, sixth, seventh, and eighth distances, the fifth distance is not equal to the sixth, seventh, and eighth distances, the sixth distance is not equal to the seventh, and eighth distances, and the seventh distance is not equal to the eighth distance. 